It is known to provide a motor vehicle having a four wheel drive mode of operation in which motive power is supplied to each of two pairs of wheels of the vehicle. Motive power is supplied to the wheels by means of a driveline.
Some known vehicles are arranged such that motive power is permanently supplied to both pairs of wheels. Some other vehicles are arranged such that motive power is selectively supplied to either only one pair or to both pairs of wheels. A driver operable selector may be provided to allow the driver to select two wheel or four wheel operation. Some driveline systems require the vehicle to be stationary when transitioning between two and four wheel drive modes. Such systems may be referred to as static disconnect/reconnect systems.
GB2407804 discloses a dynamic driveline reconnect arrangement in which reconnection of two of the wheels to the driveline following disconnection of the wheels from the driveline may be undertaken when the vehicle is moving. Such a system may be referred to as a dynamic driveline reconnect system. The system disclosed in GB2407804 employs clutch arrangements to enable dynamic driveline reconnection.
The present inventors have recognised that a problem exists with vehicles equipped with static or dynamic reconnection systems. When a four wheel drive vehicle is operated in a two wheel drive mode, a portion of the driveline remains stationary due to the fact that is has been disconnected from the gearbox. Lubricant associated with that portion of the driveline can fall in temperature or otherwise remain at a temperature that can result in relatively poor lubrication of that portion of the driveline when four wheel drive operation is subsequently resumed.
It is an aim of embodiments of the present invention to at least partially mitigate the disadvantages of known driveline systems.